It is known to drill horizontally through a pay zone to expose large areas of the production formation to a vertical wellbore and thereby increase the production rate of the well. A vertical borehole can be slanted towards the horizontal by using a whip-stock in order to offset the well using a conventional drill string; however, it is difficult to enter a thin hydrocarbon bearing formation using this technique alone. Drilling a lateral from a vertical borehole at a precise location that assures the lateral penetrating the production formation is the subject of this disclosure.
After a well has been geologized, and the payzone precisely located, a lateral borehole that extends from the vertical at the precise location required to intercept and penetrate the payzone is more likely to be made possible if an unusually small radius of curvature can be effected into the drill string extending from the casing. When this radius of curvature is known, the location of the lateral can be predicted accurately.
Method and apparatus for achieving the above desirable goals is possible by the provision of a flexible drill string that does not require a downhole motor driven bit; that can make a sharp bend to turn the vertical borehole laterally and thereafter continue to drill horizontally while being rotated by a rotary turn table of an ordinary drilling rig; and such a method and apparatus is the subject of the present invention.